1. Field of the Invention
The present invention relates to a circuit interrupter wherein an arc is interrupted by puffing a fluid for arc extention e.g. SF.sub.6 gas and more particularly, it relates to a self-arc extinction type circuit interrupter in which high pressure fluid pressurized by the arc formed between contacts, is used for performing the arc extinction.
2. Description of the Prior Arts
In the conventional circuit interrupters, a fluid in a suitable volumetric space is pressurized by the pressurizing function of arc energy transmitted from the arc to the fluid filled in the space and on the other hand, the pressurized fluid is released from an opening closed by the arc through the arc space under periodical changes of the arc current to cause a sudden decrease of arc energy in the decreasing step and to decrease a diameter of the arc whereby the arc extinction is attained by the resulting puffing and cooling effect to the arc fluid in the arc space.
In such a self-arc extinction type circuit interrupter, it is important to maintain the pressure. The pressure is dependent upon the arc energy. Accordingly, the maintenance of the pressure is relatively easy in the zone of large arc current. However, in the zone of small arc current, the arc energy is remarkably small and the pressurizing effect is low whereby the maintenance of the pressure required for the arc extinction is not easy. Accordingly, a zone of remarkably small arc extinct effect is found.
This disadvantage sets off the advantageous characteristics in the large arc current zone and moreover the arc is disadvantageously extended to a high voltage zone.